Electron tube



Nov. 23, 1937. J. T. WILSON 2,099,994

ELECTRON TUBE.

Filed May 12, 1936 2.9 v 3 l m 2 /3 HORIZONTAL Vim/64L (SA on) (RAP/D) INVENTOR JAM-IS 7'. WILSON ATTORNEY Patented Nov, 23, 1937 UNITED STATES ELECTRON TUBE James '1. Wilson, Arlington, N. 5., assig'nor to Radio Corporation of America, a corporation of Delaware Application May 12, 1938, Serial No. 19,341

7 Claims. (01. 25041.5)

or electrode and an electron emissive cathode which produces an electron beam adapted to imminous traces in accordance with the position of beam impact thereupon. The deflecting electrode system, to which this disclosure is particularly related is positioned intermediate thecathode or electron source and the. luminescent screen, and when suitable voltages are caused to act upon the beam deflecting electrodes, the

produced electron beam is caused to trace predetermined pathsacross the luminescent screen.

It is an object of the present invention to provide electrode structure for deflecting the (le veloped electron beam so that the eflects of V fringing or de-focussing of the spot and "key-j stoning are avoided. The effect of fringing or m de-focussing is well known and is corrected in the types of. tubes usually manufactured to a substantial extent through the proper design and construction of the electron gun structure: However, fringing or de-focussing of the produced :5 spot upon the screen is to some extent also produced by reason of the shaping and positioning of the deflecting electrode system, andit is an object of the present invention to overcome the fringing or de-focussing eifects which is due to .0 the electron beam deflecting system.

Keystoning, which it is also desired to correct by the present invention, is that efiect which results in electron tubes of the cathode ray type or equivalent types such as X-ray and beam tubes, 5 when the beam developed within the tube is deflected and the maximum length of traverse of the beam'under a given deflection voltage at one edge of the screen is greater or less than the extent of traverse for the same deflection voltage 0 across that portion of the screen which is diametrically opposite the first path of traverse.

This results in a pattern of traversal of the electron beam across the luminescent screen which becomes substantially trapezoidal in shape rather pinge upon a luminescent screen to produce luthan either square or rectangular, the latter depending of course upon the ratio of the deflection voltages for deflection of the beam in two mutually perpendicular planes.

Arrangements have been suggested in the prior art to overcome to some extent the detrimental fringing and keystoning effects in electron tubes of this nature, and while such schemes of. the prior art, which include the positioning of a diaphragm member between two sets of deflecting electrode members or the positioning of a ringlike structure at the edges of the deflecting electrode system most remote from the electron source,'it has been found that such structures complicate to a considerable extent the ease with which electron tubes of this type may be manufactured, and it is an object therefore of the present invention to accomplish more efliciently, while still permitting more satisfactory manufacturing methods, the effects of what is considered complicated prior art arrangements.

Other objects of the invention are naturally those of providing electron tube structure which consists of a minimum number of parts, structure which can be manufactured in quantity to a largeextent by the most simplified processes and by the aid of unskilled workmanship and, at the same time, which can be manufactured more cheaply by reason of the lack or additional electrode elements of the prior art. H

'Still other objects and advantages of this invention will, of course, suggest themselves and immediately become apparent to those skilled in the art by reading the following specification and claims in connection with the accompanying drawing in which:

Fig.- i represents schematically an electron tube of the cathode my type wherein the present invention is embodied, and

Fig. 2 schematically illustrates in a partially angular view the deflecting electrode members which are positioned withinthe electron tube shown by Fig. l. I

Now, making reference to the accompanying drawing for a further understanding of the nature of thepresent invention, the electron tube envelope U, which is preferably formed of glass or other vitreous material, of the cathode ray type has positioned at one end ofa cylindrical neck a cathode l3 which lhas a coating on its upper surface of suitablefmaterial such as barium. oxide or strontium oxide, or a combination of these compounds or the equivalent, which emits electrons copiously when heated in any suitable manner. 'For the purpose of heating the cathode I! to cause it {to emitelectrons. a

heater element l5 has been shown although it will be appreciated that the cathode element 13 may, where desired, be a directly heated cathode. In order to cause the electrons emitted from the cathode element [3 when the heater is heated to be formed into an electron beam, there is provided an anode H which ismaintained at a voltage highly positive with respect to the cathode. As the electrons leave the cathode l3 and are formed into a beam by the accelerating and focussing field produced between the anode l1 and the cathode l3, these electrons are projected longitudinally. of the tube II to impinge upon a luminescent screen l9 which is suitably supported upon the inner surface of the end wall of the tube opposite the cathode l3. As the electrons forming the electron beam impinge upon the luminescent screen structure l9, they cause it to fluoresce and phosphoresce with the result that light is produced at the point of impact of the beam. Where it is desired to control the intensity of the electron beam which impinges upon the luminescent screen 19, a grid structure 2| such, for example, as is shown by Nicolson Patent 1,417,696 may be interposed between the oathode l3 and anode l'l. Such a grid structure may consist of a suitably apertured member such as has already been shown in the art and which has not herein been illustrated in order to simplify the showing.

Other forms of intensity control of the luminescent spot produced on the tube end wall may, of course, be resorted to without invention and Where desired, it is of course obvious that electron tubes of the general type herein shown may be manufactured without the inclusion of the grid member, and such tubes, for example, would find particular application in oscilloscope work where it is not usually desirable or necessary to control the intensity of the resultant luminous effect, although for television usage of a cathode ray tube of the type herein disclosed, a grid or equivalent intensity control becomes desirable in order to produce shading effects in the resultant luminescent trace of the electron beam.

As theelectrons forming the electron beam are drawn from the cathode I3 and formed into a beam by the application of voltages to the anode ll, these electrons are arranged to pass through diaphragm members 23 and 25 positioned in the tubular anode ll. These diaphragm members are suitably apertured at their centers and serve to limit to some extent at least the crosssectional area of the resultant electron beam. After the electron beam has passed through the diaphragm members 23 and 25 of the first anode H, the beam is then subjected to the action of an electrostatic focussing field produced by the cooperative action of the first anode l1 and a second anode 21. The second anode 21 is maintained highly positive with respect to the first anode H, the ratio of the voltage of the first anode and second anode to the cathode l3 usually being of the order of four to one, or thereabouts, although with respect to this voltage ratio, some degree of tolerance is permissible.

The second anode 21, as shown by the accompanying drawing, is formed'as a metallic coating on the interior surface of the neck of the tube I I, and is shown as continuing through the neck of the tube to a plane substantially corresponding to the plane of termination of the tubular first anode ll. of course, it will be obvious that the second anode structure may be in the form of a second tubular metallic member deflecting plate 33.

which is supported in axial alignment with the first anode l1 and thus forming a separate electrode member in the path of the developed electron beam and adjacent the first anode although positioned with greater longitudinal spacing from the cathode than the first anode. It will also be appreciated that the second anode while formed as a coating on the interior surface of the neck portion of the tube Il may be terminated at a plane even beyond the edge of the deflecting electrode most remote from the cathode, and it will also be appreciated of course that the coating, which serves as the second anode, on the interior surface of the tube may extend throughout substantially the entire length of the cone portion of the inner surface, although these latter suggestions furnish mere modifications and are not illustrated because of the obvious nature of the same to those skilled in the art and because further showing is unnecessary to a complete understanding of the true nature of the present invention.

In order to deflect the produced electron beam which is projected beyond the first anode IT and through the second anode 21 so that the produced electron beam traverses the screen l9, there is providedtwo sets of deflecting electrodes 29, 3| and 33, 35 which move the beam in two mutually perpendicular directions. The electrodes 29 and 3| are preferably those electrodes which cause the beam to move relatively slowly in one direction across the screen and are each formed as a rectangular or square shaped plate. The deflecting electrode members 33 and 35 are those two electrode members which are arranged to deflect the produced electron beam in a direction perpendicular to the direction of deflection because by the deflecting electrodes 29 and 3i, and these electrodes are shaped so that one of the deflecting electrodes 33 is preferably a flat surface whose edge 31 nearest the electron source is curved concavely with respect to the electron source. The electrode 35 has its edge portion 31 nearest to the electron source also curved con-.

cavely with respect to the source, and this is of a curvature corresponding to the curvature of the In addition, the electrode 35 has its edges, which are parallel to the axis of the tube, provided with flange members 39 extending in the direction of the deflecting plate 33. These flanged edges 39 are formed by bending over the edge of the deflecting plate 35 or by welding to the deflecting plate 35 a narrow flange element. It, however, should be understood that the flat area of the plate 35 corresponds to the flat area of the plate 33 and, therefore, in form ing the deflecting electrode member 35 where it is desired to form the flange by bending the electrode member 35 is of slightly greater transverse dimension than the electrode member 33.

When the tube of the type herein disclosed is in operation, the deflecting electrode members 39 and 33 are preferably connected by way of cor!- ductors '31 and 39 with the conductor 4| arranged to supply positive potential with respect to the cathode to the second anode member 21. For convenience, this arrangement has been shown by providing a ground connection 43 having all of the conductors 38, 39, and 4|, in which condition it will be appreciated that the cathode I3 is, for example, operated well below ground potential, the exact voltage being such that the ratio of the second to first anode voltage and first anode to cathode voltage satisfies the operational condition to providesuitable focussing and acceleration of the electron beam.

From the foregoing, it will be appreciated that the electron beam as it passes between the deflecting plate pairs 29 and 3| is caused to move in the plane of the drawing when voltages are supplied between the electrodemembers 3| and 29, and similarly when voltages are'supplied to the deflecting electrode members 35 and 38, the

produced electron beam is caused to move in and out of the plane of the paper looking at the showing in Fig. 1. As the beam is moving, the curvature of the plates 33 and 35 shown by the curve 31 will correct for the de-focussing or fringing effects which would normally be due to unequal sensitivity of deflection for the beam as it is moved by the deflecting electrode pair 29 and 3|. The curvature, as shown by the curved edge 31 in the drawing, is preferably such that the radius from which the curve portion 31 is struck is equal to the distance from the point of initial beam deflection to the innermost portion of the curve 31, as shown for example by the dash-dot line on the drawing in Fig. 1. The flange portion of the electrode member 35 will correct for the keystoning because of the fact that the sensitivity of deflection, that is, the effective voltage applied to the deflecting electrode to deflect the electron beam within a given distance is greater at the edge than at the innermost portion of the plate.

In the light of the foregoing, it of course will be obvious to those skilled in the art that various modifications and changes may be made without departing from the spirit and scope of the present invention, and it is therefore believed that any and all of such modifications may be made as fall fairly within the spirit and scope of the hereinafter appended claims.

Having now described my invention, what is claimed and desired to secure by Letters Patent is the following:

1. In an electron tube, means to develop an electron beam, a plurality of electrodes to deflect said electron beam, said electrodes each having one edge portion thereof concavely curved with respect to the origin of the produced electron beam, and an inwardly extending flange attached to the opposite edges of one of said electrodes, said flange extending parallel to the direction of beam motion.

2. In an electron tube, an electron source, an accelerating electrode and a luminescent screen, a pair of electrostatic deflecting electrodes positioned intermediate the accelerating electrode and the luminescent screen, said pair of deflecting electrodes each having the inner edge portion'thereof which is positioned towardsaid cathode concavely curved with respect to said cathode, and flange members attached to one of said deflecting electrodes, said flanges being attached to the edges of said electrode extending parallel to the longitudinal axis of said electron tube.

3. The electron tube structure claimed in claim 2 wherein said flanges extend inwardly toward the opposite deflecting member.

4. The electron tube structure claimed in claim 2 comprising, in addition, a second pair of plate electrodes for deflecting the electron beam perpendicularly to the path of said first-named deflecting electrodes, said last-named electrodes being positioned intermediate the first-named set of deflecting electrodes and the source.

.5. An electron tube comprising an electron source, an accelerating electrode and a luminescent screen upon which the electron beam developed by the co-operative action of said electron source and accelerating electrode is adapted to impinge to produce luminous effects, a pair of oppositely positioned substantially flat deflecting plate electrodes located intermediate the accelerating electrode and the luminescent screen, each of said plate electrodes having the edge portion thereof which is toward said electron source curved at a predetermined radius of curvature, and a flange member attached to opposite edges of one of said deflecting plate members, said flanges being positioned longitudinally of the tube axis and attached to the edges of the plate electrode in such manner as to extend in the direction toward the plate electrode member opposite the same.

6. In an electron tube, an electron source, an

anode adapted when positive voltages are applied thereto relative to the electron source to produce an electron beam, a luminescent screen positioned in the path of the developed electron beam and adapted to become luminous at points of impact of the developed electron beam, a pair of electrostatic deflecting plate electrodes positioned intermediate the electron source and the luminescent screen, a second pair of electrostatic deflecting plate electrodes positioned intermediate said flrstnamed pair of deflecting plates and said luminescent screen, said second-named deflecting electrodes each having the edge portion toward said electron source curved at a radius of curvature measured from the point of initial deflection of said electron beam through said first-named deflecting electrodes, and a flange member connected with opposite edge portions of one of said last-named deflecting plate electrodes so that the flange members extend longitudinally of the tube axis and in the direction of the second electrode of said last named pair of deflecting plate electrodes.

'7. In an electron tube having electron beam developing means and a plurality of pairs of mutually perpendicular electron beam deflecting plates for deflecting the developed electron beam in two mutually perpendicular directions under the application of potentials applied thereto, the

method of compensating for distortion due to deflection which comprises applying to the first set of deflecting plates potentials to develop a substantially uniform electrostatic fleld for deflecting the developed electron beam in a first direction, applying potentials to the second pair of deflecting electrodes for developing a non-uniform electrostatic fleld for deflecting the developed electron beam in a direction substantially perpendicular to the first direction of deflection and producing between'the electrode, pairs for deflection in each of said directions a non-uniform electrostatic field.

JAMES T. WILSON. 

